The invention to which this application relates is to the application of a coating to a substrate involving the improved utilisation of an exciting medium.
The use of excitation mediums is known in the application of coatings. However, deleterious effects of high energy species can be present within the “exciting medium”, such as bombarding ions and UV photons. This can prevent the coating of sensitive substrates with films that retain a significant degree of monomer functionality and can also cause ion etching effects.
The exciting medium tends to be the medium in which, conventionally, the substrate to be coated is positioned. The exciting medium can be generated in a number of ways, the most common of which is the generation of a plasma, with the area over which the plasma is said to extend typically defined by a plasma glow typically Iying within the area defined by the electrodes used to generate the plasma. The positioning of the plasma within the exciting medium is typically referred to as direct PECVD as defined in the book “Cold Plasma in Materials Fabrication—Alfred Grill—IEEE Press 1993”. The same book also described the provision of remote PECVD, in which the substrate to be coated is removed from the exciting medium. However in both cases the coating is achieved through the introduction of gaseous materials and this slows the deposition rate significantly and renders the same commercially unviable for many applications.
It is also known from earlier patents such as U.S. Pat. No. 5,451,260 and WO9810116 that the substrate can be positioned in the same CVD reactor as a nozzle for introducing material for the coating process but neither patent acknowledges the possible use of atmospheric-pressure plasmas, pulsed plasmas and continuous processing.
The patent application WO 0228548 describes a direct PECVD process, wherein in the examples of the invention, the sample to be coated is placed within the plasma and hence the exciting medium formed from atomised coating forming material. In addition the patent application does not mention low-pressure or pulsed plasmas or other types of remote plasma and the possibility of non-ionised or non-plasma excitation sources (such as ozone, radicals, UV irradiation or heat). Furthermore in this patent application the nozzle for introducing the coating material is positioned at the plasma region to introduce the material within the plasma and directly impinges upon the substrate.
Patent application WO 0070117 does not use an atomiser but does use plasmas (high and low pressure) to deposit coatings on a remote substrate. However, the pressure range specified in Claim 15 (10-1000 Torr) is 10 to 100 times higher than that normally used for low-pressure glow discharge deposition, no alternative means of excitation are mentioned and no specific examples of polymeric coatings and their uses are cited.
The aim of the present invention is therefore to provide a means of using an atomiser to inject a liquid or liquid/solid slurry into an exciting medium to allow rapid deposition, even from involatile monomers onto substrates or a substrate to be coated with improved deposition rates and coating quality so as to render the same commercially viable.